Silica zeolite low-k dielectric thin films and methods for their production

ABSTRACT

Thin films for use as dielectric in semiconductor and other devices are prepared from silica zeolites, preferably pure silica zeolites such as pure-silica MFI. The films have low k values, generally below about 2.7, ranging downwards to k values below 2.2. The films have relatively uniform pore distribution, good mechanical strength and adhesion, are relatively little affected by moisture, and are thermally stable. The films may be produced from a starting zeolite synthesis or precursor composition containing a silica source and an organic zeolite structure-directing agent such as a quaternary ammonium hydroxide. In one process the films are produced from the synthesis composition by in-situ crystallization on a substrate. In another process, the films are produced by spin-coating, either through production of a suspension of zeolite crystals followed by redispersion or by using an excess of the alkanol produced in preparing the synthesis composition. Zeolite films having patterned surfaces may also be produced.

BACKGROUND OF THE INVENTION

This invention relates to the provision of new low-k dielectric filmsfor use in semiconductor and integrated circuit devices.

With the continuing decrease in size of microprocessors, low-kdielectrics are required to address some of the challenging problemssuch as cross-talk noise and propagation delay. These can become morecritical to performance and more difficult to overcome as overallsemiconductor device size is decreased while capabilities are increased.Among other aims, the industry is engaged in a search for dielectricshaving a lower k value than dense silicon dioxide (k=3.9-4.2). Theindustry expects that low-k dielectric materials, especially materialswith a k value lower than 3, and optimally lower than 2.2, will beneeded for the design of devices with very small, e.g., 100 nm,features. In addition to the low k value, new dielectric materials mustalso meet integration requirements. These include a thermal stability inexcess of 400° C., good mechanical properties, good adhesion to avariety of surfaces and substrates, low water uptake and low reactivitywith conductor metals at elevated temperatures.

A great number of materials have been proposed and studied as potentialcandidates, including some that demonstrated k values of 2 or lower. Twomajor classes of such materials are dense organic polymers and porousinorganic-based materials. Some dense organic polymers (e.g., highlyfluorinated alkane derivatives such as polytetrafluoroethylene) may havesufficiently low k values, but they have the disadvantages of havingrelatively low thermal stability, thermal conductivity, and mechanicalstrength. In addition there is concern that they may react withconductor metals at elevated temperatures.

Among porous inorganic-based low-k materials, sol-gel silica has beenextensively studied and is commercially available, for example fromAllied Signal or Honeywell under the trademark Nanoglass. Sol-gel silicaoffers tunable k values, but some major concerns have been cited. It hasa relatively low mechanical strength and a wide pore size distribution.Heat conductivity can be a shortcoming, especially with highly poroussol-gels, and this product also can possess a low resistance toelectrical breakdown because of some randomly occurring large pores. Inaddition, its pore surfaces are initially hydrophilic, and requiresurface treatment to avoid absorption of moisture.

Recently, surfactant-templated mesoporous silica has been studied forlow-k dielectric applications. Such materials are described, forinstance, by Zhao, et al., Adv. Mater. 10, No. 6,1380 (1998) andBaskaran et al., Adv. Mater. 12, No. 4,291 (2000). This class ofmaterials has more uniform pores than sol-gel silica (with a range ofpore size of up to about 100 nm) and has been shown to have promising kvalues. Like sol-gel silica, however, there are concerns around lowmechanical strength and hydrophilicity.

Hydrogen silsesquioxane films have also been under consideration for useas low-k dielectrics. Resins of this type, from which the films areproduced, have been described in Lu et al., JACS 122, 5258 (2000) and anumber of patents, including the recent U.S. Pat. No. 6,210,749. Aseries of these has recently been introduced under the trademarks FOxand XLK by Dow Corning. The FOx products are non-porous and have a kvalue of about 2.9. By incorporating porosity through a complexthree-step process involving a high boiling organic solvent and ammoniagellation, XLK films with a lower k value of about 2.0-2.3 can beproduced. Other Dow Corning products recently introduced include atrimethylsilane-containing gas (sold under the trademark Z3MS CVD) whoseapplication by chemical vapor deposition can variously produce thin filmdielectrics comprised of silicon oxycarbide or silicon carbide. Suchtechnology is described, for instance, in U.S. Pat. No. 6,159,871.However, the k values of such films do not reach the lower end of thedesirable range.

It would be advantageous, in light of these developments, to provide alow-k dielectric material that can be applied as a thin film, hasrelatively small pores (most preferably <5 nm) and uniform poredistribution, with the necessary mechanical strength to be treated bychemical and mechanical polishing (CMP). Preferably, also, such filmswill have low hydrophilicity or can readily be modified to have lowhydrophilicity, so that they would be relatively unaffected by thepresence of moisture.

BRIEF SUMMARY OF THE INVENTION

This invention comprises the provision for use in semiconductor devices,of films that are comprised of silica zeolites, as well as methods formaking such films, and articles such as semiconductor devices that useor include them.

In one aspect, the invention comprises a semiconductor device having asubstrate and one or more metal layers or structures located on thesubstrate, and further including one or more layers of dielectricmaterial, in which at least one layer of dielectric material comprises asilica zeolite.

In a second aspect the invention comprises a method for producing asilica zeolite film on a semiconductor substrate comprising forming thefilm by in-situ crystallization, and, as a product, a semiconductorsubstrate or device having one or more films so produced.

In a third aspect the invention comprises a method for producing asilica zeolite film on a semiconductor substrate comprising forming thefilm by spin coating, and, as a product, a semiconductor substrate ordevice having one or more films so produced.

In another aspect the invention comprises a method of production ofsilica zeolite films having surface patterns, and, as a product, asemiconductor substrate or devices having one or more films so produced.

In a further aspect the invention comprises certain silica zeolite filmsthat are novel per se.

DESCRIPTION OF THE DRAWINGS

FIG. 1 comprises three SEM scanning electron microscope micrographs ofpure-silica MFI films on a silicon wafer produced by in-situcrystallization: (a) before polishing, top view, (b) after polishing,top view, (c) after polishing, cross-sectional view. “MFI” is a codedesignation issued by the International Zeolite Association for zeoliteshaving a specific topology, i.e. channel or pore structure.

FIG. 2 depicts X-ray diffraction patterns for a pure-silica MFI film ofFIG. 1 and a powder MFI sample for comparison.

FIG. 3 depicts dependence on exposure time to air with 60% relativehumidity of the dielectric constant k of a calcined pure-silica MFI filmas shown in FIG. 1, and of one that has been treated by silylation.

FIG. 4 depicts the dielectric constant as a function of frequency for acalcined pure-silica MFI film produced by in-situ crystallization of thefilm of FIG. 1 and a film produced by spin-on of redispersed MFInanocrystals.

FIG. 5 shows the dependence of the dielectric constant (k) of anas-synthesized pure-silica MFI film of FIG. 1 on exposure time to air,with 60% relative humidity.

FIG. 6 comprises three SEM micrographs of spin-on pure-silica MFI filmsproduced using a colloidal suspension of nanocrystals: (a) as-deposited,top view, (b) after microwave treatment, top view, (c) after microwavetreatment, cross-sectional view.

FIG. 7 comprises four SEM micrographs of pure-silica MFI films producedby spin-on of redispersed MFI nanocrystals: (a) top view of a film withone spin; (b) cross-sectional view of a film with one spin; (c)cross-sectional view of a film with three spins (d) cross-sectional viewof a film with four spins.

FIG. 8 comprises six SEM micrographs of pure-silica MFI films producedby spin-on of redispersed MFI nanocrystals that were treated withsecondary growth by microwaves, with different treatment times.

FIG. 9 depicts IR spectra of pure-silica MFI films produced by spin-onof redispersed MFI nanocrystals that were (a) untreated and (b) treatedwith microwaves after production.

FIG. 10 depicts X-ray diffraction patterns for films in FIG. 9.

FIG. 11 depicts the dependence of the k value on the exposure time toair of 60% relative humidity for a pure-silica MFI film produced byspin-on with 3 spins of redispersed MFI nanocrystals.

FIG. 12 comprises three SEM micrographs of pure-silica MFI filmsprepared by a spin-on process conducted without redispersion of zeolitecrystals.

FIG. 13 shows the dependence of the dielectric constant (k) of anas-synthesized pure-silica MFI film of FIG. 12 on exposure time to air,with 50-60% relative humidity.

FIG. 14 depicts dielectric constant as a function of frequency for acalcined pure-silica MFI film produced from the film of FIG. 12.

FIG. 15 depicts nitrogen adsorption-desorption isotherms of two bulksilica samples dried using two procedures: static drying (FIG. 15a) andflow-air drying (FIG. 15b)

FIG. 16 depicts powder X-ray diffraction patterns for bulk materialsfrom a zeolite nanoparticle suspension taken at wide and low angles.

FIG. 17 comprises four SEM micrographs showing surface-patterned silicazeolite films.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to the production and use of thin films of silicazeolites in integrated circuit and semiconductor assemblies orsubstrates, and for other uses as described herein. The term “silicazeolites” refers to zeolites having only or substantially only siliconand oxygen, and very little or no aluminum or other metals typicallyfound in zeolites. For the purposes of this invention, silica zeolitescan contain minor amounts of aluminum or other metals, that is, amountsthat do not adversely affect the properties or performance of theresulting films. Silica zeolites of this type are generally referred toas “high-silica MFI zeolites”. However, it is preferred that pure-silicaMFI zeolites are used in this invention. “Pure-silica MFI zeolites” aresilica zeolites having only silicon and virtually no aluminum or othermetals. One type of pure-silica MFI zeolite preferred for use in thisinvention, known as silicalite, is described in Flanigen, et al.,Nature, 271, 512 (1978). Other silica zeolites that may be used in thisinvention include BEA, MCM-22, and MTW. Silica zeolites suitable for usein this invention may be produced either using starting materialscontaining only silicon and no metals, or may be produced bydemetallation, particularly dealumination, of zeolites that containaluminum or other metals.

Zeolites in general are microporous crystalline materials with generallyuniform molecular-sized pores that have been described in general ashaving low theoretical dielectric constants [e.g., Haw, et al., Nature1997, 389, 832 and van Santen, et al., Chem. Rev. 1995, 95, 637.]. Theirpore size (<2 nm) is significantly smaller than sizes of typicalfeatures of integrated circuits. Zeolites have higher heat conductivity(0.24 W/m° C.) than sol-gel silica due to their dense crystallinestructure. Unlike organic polymers and inorganic-organic composite low-kmaterials, pure silica is also known for its compatibility with currentsemiconductor processes.

Some types of silica zeolite films are known. The production and uses ofsilica zeolite films are described, for instance, in Jansen, et al.,Proc. 9^(th) Intl. Zeolite Conf. (Montreal, 1992) and J. Crystal Growthvol. 128, 1150 (1993), Koegeler et al., Studies in Surface Science andCatalysis, vol. 84, 307 (1994) and Zeolites 19, 262 (1997) and den Exteret al., Zeolites vol. 19, 13, (1997). They also are described in a 1999review article entitled “Zeolite Membranes” by Tavolaro et al. (Adv.Mater. vol. 11, 975). At least some of these films were produced, forinstance, by a process similar to the in-situ crystallization processdescribed herein. However, in all these publications the zeolite filmswere prepared for uses other than in semiconductor or electronicdevices—uses that are typical and known for zeolites, for instance ascatalytic membranes, for the separation of gases or liquids, or forchemical sensors. In some cases the films were prepared on siliconwafers, among other types of supports. However, there is no mention inany of these publications of the suitability of them for use insemiconductor devices. One publication of two of the present inventorsand others discloses production of patterned pure-silica MFI films usinga stamp, with a suggestion that they may be useful in microelectronicand optoelectronic applications [Huang et al., J.A.C.S. vol. 122, 3530(2000)].

In one aspect, this invention thus comprises providing a semiconductordevice that comprises a semiconductor substrate, one or more metallayers or structures, and one or more dielectric films, wherein at leastone dielectric film comprises a silica zeolite film.

By “semiconductor substrate” is meant substrates known to be useful insemiconductor devices, i.e. intended for use in the manufacture ofsemiconductor components, including, for instance, focal plane arrays,opto-electronic devices, photovoltaic cells, optical devices,transistor-like devices, 3-D devices, silicon-on-insulator devices,super lattice devices and the like. Semiconductor substrates includeintegrated circuits preferably in the wafer stage having one or morelayers of wiring, as well as integrated circuits before the applicationof any metal wiring. Indeed, a semiconductor substrate can be as simplea device as the basic wafer used to prepare semiconductor devices. Themost common such substrates used at this time are silicon and galliumarsenide.

The films of this invention may be applied to a plain wafer prior to theapplication of any metallization. Alternatively, they may be appliedover a metal layer, or an oxide or nitride layer or the like as aninterlevel dielectric, or as a top passivation coating to complete theformation of an integrated circuit.

At least two different processes may be used to prepare the silicazeolite films and the semiconductor devices that include them. These arein-situ crystallization and the spin-on technique.

In both processes, a silica zeolite synthesis composition is firstformed by combining a silica source with an organic zeolite-formingstructure-directing agent (“SDA”). The silica source is preferably anorganic silicate, most preferably a C₁-C₂ orthosilicate such astetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS).However, inorganic silica sources such as fumed silica, silica gel orcolloidal silica, may also be used. The zeolite-formingstructure-directing agent is typically an organic hydroxide, preferablya quaternary ammonium hydroxide such as tetrapropylammonium hydroxide(TPAOH), tetraethylammonium hydroxide (TEAOH), triethyl-n-propylammonium hydroxide, benzyltrimethylammonium hydroxide, and the like. Theresulting synthesis composition contains ethanol, if TEOS is used as thesilica source, or methanol, if TMOS is used.

In the in-situ crystallization process of this invention, the molarcomposition of the synthesis composition is xSDA/1 silica source/yH₂O. Xcan range from about 0.2 to about 0.6, preferably from about 0.2 toabout 0.45, and most preferably 0.32. Y can range from about 100 to 200,preferably from about 140 to about 180 and is most preferably 165.

In the in-situ crystallization process, in general, the substrate to becoated is brought into contact with the synthesis composition inside areaction vessel such as an autoclave. The vessel is then sealed andplaced in an oven. If a convection oven is used, heating is generallyconducted at a temperature of from about 120° C. to about 190° C.,preferably from about 160° C. to about 170° C. and most preferably about165° C. A microwave oven can also be used, in which case the power levelis preferably high and the time is from 5 to 30 minutes, preferably 10to 25 minutes, and most preferably about 10 minutes. The drying step ispreferably followed by heating conducted at temperatures of from about350° C. to about 550° C., preferably from about 400° C. to about 500° C.This heating step, usually referred to as a calcination step,accomplishes removal of the SDA from the film and can improve the film'sadhesion and strength.

Films produced by this process generally have a k value of less than3.3, in some cases as low as about 2.7. The film thickness is generallyless than about 1000 nm, preferably less than about 500 nm.

The films produced by this process are generally hydrophobic;consequently, their properties are relatively uninfluenced by moisture.If desired, hydrophobicity may be increased further by removal ofsurface hydroxyl groups by silylation, for instance, withchlorotrimethylsilane, as described below, by high temperatureoxidation, or by other techniques known in the art for this purpose.

There are two embodiments of the spin-on process, one involvingredispersion of zeolite crystals, the other not involving thistechnique.

In the first embodiment, a zeolite synthesis composition containing anSDA, a silica source (as described above) and water is prepared. Themolar composition of the synthesis composition is x₁ SDA/1 silicasource/y₁ H₂O. X₁ can range from about 0.2 to about 0.5, preferably fromabout 0.3 to about 0.4, and most preferably 0.36. Y₁ can range fromabout 5 to about 30, preferably from about 10 to about 20, and mostpreferably 14.29.

In conducting this process, the above synthesis composition is prepared.Then the composition is loaded in a vessel, which is sealed, and thecomposition is heated to a temperature of from 40 to 100° C., preferably60-90° C. and most preferably 80° C. The heating time is from 1 day to 7days, preferably 2-4 days, and most preferably 3 days. A suspension ofzeolite crystals is produced.

In this embodiment, the suspension is then centrifuged or otherwisetreated to recover nanocrystals (i.e., nanometer-sized crystals). Thecrystals are then redispersed in ethanol or another appropriatedispersant, and are placed on a substrate that is situated on a spincoater. Spin coating is then conducted as known in the art by rotatingthe substrate at high speeds such that a highly uniform film is obtainedon the substrate. Preferably the film is subjected to a brief dryingstep (e.g. about 10-12 minutes at 100° C.). Finally the film issubjected to a heating (“calcination”) step. This step is conducted attemperatures of from about 350° C. to about 550° C., preferably fromabout 400° C. to about 500° C. It accomplishes removal of the SDA fromthe film and can improve the film's adhesion and strength.

In another embodiment of the spin-on process, involving a spin-on ofas-synthesized nanoparticle suspension, methanol or ethanol is includedin the initial synthesis composition. If a lower alkyl orthosilicate isused as the silica source, methanol or ethanol is chosen ascorresponding to the alkyl groups. This is in addition to any amountformed by the hydrolysis of the organic silica source. If an organicsilica source is used, either methanol or ethanol may be used. The molarcomposition of the synthesis composition if x₂ SDA/1TEOS/z₂ EtOH(orMeOH)/y₂ H₂O. X₂ can range from about 0.2 to about 0.5, preferably fromabout 0.3 to about 0.4, most preferably 0.36. Y₂ can range from about 10to 20, preferably from about 12 to about 18, most preferably 14.29. Z₂can range from about 1 to about 10, preferably from about 2 to about 6,most preferably 4.0.

In this embodiment it is not necessary to collect and then redispersethe zeolite nanocrystals, and the suspension (without redispersion) issubjected to spin coating as described above, followed by optionaldrying and then heating or calcination.

Films produced by the spin-on process of this invention generally have ak value of less than 3.2, and in some cases the k value may be as low asabout 2.1. The film thickness is generally less than about 800 nm,preferably less than about 500 nm.

The films produced by the spin-on process of this invention are newtypes of silica films that are distinct from those previously producedby Jansen and others and described in the publications mentioned above.Those films produced in the past were often not completely continuous.However, even when successfully produced as continuous films, they had(as is typical for zeolites) a single, relatively uniform, pore size—anaverage pore size of about 5.5 Angstroms (this size was generallyreferred to as “micropores”), The total porosity of such films (ratio ofpore volume to total film volume) was about 30-33%

On the other hand, films produced by both embodiments of the spin-onprocess described herein are continuous bimodal films, having bothmicropores, as defined above, and larger pores, generally termedmesopores. These films are novel per se, and may be used not only insemiconductor structures as described herein, but also for other usesknown for zeolite films such as catalytic membranes, separation of gasesor liquids, and chemical sensors.

The micropores of these novel films have an average pore size of about5.5 Angstroms and a total pore volume of from about 0.15 to about 0.21cm³/g. The mesopores have an average pore size of from about 2 to about20 nm, preferably from about 2 to about 10 nm, most preferably about 3nm. Total pore volume of the mesopores is from about 0.1 to about 0.45cm³/g, preferably from about 0.2 to about 0.3 cm³/g, and most preferablyabout 0.25 cm³/g. The total porosity of these novel films is about 50%.

When the zeolite precursor or synthesis composition is formed usingexcess ethanol or methanol, as above, the resulting suspension may alsobe used to produce silica zeolite films having surface patterns. Ethanolis preferred for this process. Here, instead of in-situ crystallizationor spin coating, the suspension is simply deposited on an appropriatesubstrate and allowed to dry at ambient temperatures. Surface patternsare believed to form spontaneously as a result of convection due to theevaporation of the excess ethanol. Eventually the suspension driescompletely, and the zeolite nanoparticles become locked into solidpatterns. The use of ethanol as opposed to another alcohol such aspropanol, the presence of excess ethanol in the system (as opposed toonly the amount generated between the template and the silica source),and the crystal size in the suspension, are important factors in theproduction of surface-patterned silica zeolite films by this process.Preferably, the suspension contains crystals of about 25-50 nm diameter,as well as smaller nanoslabs and nanoslab aggregates.

Patterned films produced by the above process are not necessarilydisposed in very thin layers, because they have not undergone steps suchas spin-on coating to render them so. In addition, they do notnecessarily possess k values as low as other films described herein.However, they are considered useful for electronic and otherapplications.

As described below, the properties of silica zeolite films produced byspin-coating can be varied in several ways. The film thickness can beincreased, if desired, by conducting the spin-on process two or moretimes, with additional material added on each occasion. If the film isproduced by the first embodiment of the spin-on process, that is, one inwhich crystals are redispersed before the spin-on is conducted, theadhesion of the film to the substrate may not be strong enough towithstand treatments such as mechanical polishing. If that is the case,the calcined film can be treated by exposing it to microwaves in thepresence of additional zeolite synthesis or precursor solution, or byheating it with additional zeolite precursor solution in a convectionoven or similar equipment. This produces a secondary growth of zeoliteon the substrate, but if the treatment is kept reasonably brief (perhapsless than 15 minutes for microwaving), the film thickness does notsignificantly increase.

The films produced by the spin-on processes also are generallyhydrophilic. To minimize or prevent adverse affects due to moisture,these films may be made substantially hydrophobic by treatments toremove surface hydroxyl groups, such as by silylation (withchlorotrimethylsilane, for example), high temperature oxidation, orother techniques known in the art for this purpose.

The following examples are provided to illustrate the invention.However, these examples are included as illustrative only, and not withthe intention or purpose of limiting the invention in any way.

EXAMPLE 1

This example illustrates an in-situ crystallization process forproduction of pure-silica MFI films and describes properties of thefilms so produced.

Thin (controllable between 250-500 nm) b-oriented pure-silica MFI filmswere prepared on a silicon wafer by in-situ crystallization using aclear synthesis composition with the molar composition being 0.32TPAOH:TEOS: 165H₂O (TPAOH=tetrapropylammonium hydroxide;TEOS=tetraethylorthosilicate). A clean-room grade wafer was used,without further cleaning. The wafer (2×2 cm) was fixed in a Teflon-linedParr autoclave. Crystallization was carried out in a convection oven at165° C. for 2 hours. As-synthesized film samples were rinsed withdeionized water and blow-dried with air. Removal of the organicstructure-directing agent (tetrapropylammonium hydroxide) was carriedout by calcination at 450° C. for 2 h under air. Pure-silica MFI thinfilms of equal quality were successfully prepared on low-resistivitysilicon (for capacitance measurement), high resistivity silicon (fortransmission FT-IR measurement), silicon nitride and silicondioxide-covered wafers.

FIG. 1 shows SEM micrographs of a pure-silica MFI film produced byin-situ crystallization on a low resistivity silicon wafer. The film iscontinuous, and predominantly b-oriented (FIG. 1a). The orientation ofthe film was confirmed by x-ray diffraction (FIG. 2). Some twinnedpure-silica MFI crystals are present. These can cause minor surfaceroughness. However, a smooth surface can be obtained by simple polishingfor about 10 min with 0.05 μm alpha-Al₂O₃ suspension using a Buehlerpolisher. The polished film (FIG. 1b) is shiny and shows a uniformcharacteristic green color consistent with its thickness. No crack orfilm delamination was observed during polishing, indicating that thefilm has excellent mechanical strength and adhesion, and is potentiallycompatible with chemical mechanical polishing (CMP). A cross-sectionalSEM micrograph shows that the polished film has a uniform thickness of320 nm (FIG. 1c).

The pure-silica MFI film so obtained has an elastic modulus of 30-40 GPa(by nanoindentation). The modulus of sol-gel based films, on the otherhand, is often less than 6 GPa. A modulus of 6 GPa is usually considereda threshold value for low-k dielectrics. The modulus of mesoporoussilica has been reported to be in the range of 14-17 GPa for a porosityof ˜55% and it is expected that the modulus will decrease with porosity.Dense silica has a modulus of about 70 GPa.

To measure the dielectric constant of the film, aluminum dots with adiameter of 1.62 mm and a thickness of 1 μm were deposited on a polishedpure-silica MFI film using thermal evaporation deposition through ashadow mask. The reverse side of the sample was etched with bufferedhydrofluoric acid to remove pure-silica MFI film; then a layer ofaluminum was deposited by evaporation. The dielectric constant of thepure-silica MFI film was calculated by measuring the capacitance of theaforementioned metal-insulator-metal structure using a Solartron 1260impedance analyzer combined with standard Signatone probe station andmicropositioner. Four aluminum dots were usually deposited and theaverage k value reported. The film sample was dried at 120° C. overnightand saved in a desiccator before capacitance measurement. A dry nitrogenblanket was also applied during capacitance measurement to minimizewater adsorption. As-synthesized and calcined films were shown to havedielectric constant values of 3.4 and 2.7 and dielectric loss tangentsof 0.013 and 0.018 at 1 MHz, respectively. There is little change of kversus frequency at around 1 MHz (FIG. 4). The k value of the calcinedfilm is consistent with the known porosity of pure-silica MFI (33%).

The effect of water adsorption on the k value of a pure-silica MFI filmprepared by this process was examined by exposing the sample to air at60% relative humidity and monitoring the k value versus exposure time.As expected, there is no change of the k value with exposure time (FIG.5).

Transmission FT-IR (Bruker Equinox 55) measurements were conducted onpure-silica MFI films prepared on a high-resistivity wafer. Only a veryweak water adsorption band was detected in the calcined samples; this isconsistent with the k value measurement.

EXAMPLE 2 Spin-coating with Redispersed Zeolite Nanocrystals

To reach ultra-low k values, the porosity of a pure-silica MFI film canbe increased using spin-coating, a process that the currentsemiconductor industry regards as more friendly than in-situcrystallization. This type of silica zeolite film has a higher porosityowing to the presence of inter-nanocrystal packing voids.

Pure-silica MFI nanocrystals were prepared by the procedure reported inHuang, et al., above; Wang, et al., Chem. Commun., 2333 (2000), asfollows. A synthesis composition was prepared by dropwise addition ofaqueous TPAOH solution into TEOS with strong agitation, followed by 3days of aging at 30° C. under stirring. The molar composition of thefinal clear solution was 0.36 TPAOH: TEOS: 14.29 H₂O. The clear solutionwas loaded into a polypropylene bottle and heated at 80° C. for 3 days,with constant stirring at 250 rpm. The resulting colloidal nanocrystalswere recovered by repeated cycles of centrifugation at 15,000 rpm. Thecentrifugate was recovered after decanting the upper solution, and theproduct was redispersed in pure water under ultrasonic treatment. Thecycle was repeated until the supernatant liquid had a pH<8. Finally theproduct was redispersed in ethanol for use in spin coating. Nanocrystalsso obtained have a uniform diameter of about 50 nm. A Laurell spincoater was used, with a spin rate of 3000 rpm.

During the spin coating, the pure-silica MFI nanocrystals self-assembledinto a uniform film. This is thought to be a result of hydrogen bondingof pure-silica MFI surface hydroxyl groups while ethanol was evaporated.SEM images show that the films thus produced have a smooth surface witha close-packed structure (FIG. 6a) and a uniform thickness of 290 nm.The film thickness can be controlled by adjustment of the solid loadingof the suspension. The film was calcined at 450° C. for 2 h to removethe organic structure-directing agent. N₂ adsorption was performed onbulk material obtained using a similar drying procedure and revealedthat the film had a uniform inter-particle particle pore size of 17 nmand inter-particle pore volume of 0.40 cm³/g. Capacitance measurementshowed that calcined spin-on films have a k value of 1.8-2.1, namely onethat reaches the ultra low-k range. The dielectric loss tangent of thesefilms is about 0.0075. The k value changes little with frequency ataround 1 MHz

EXAMPLE 3 Variation in Spin Number

Experiments were conducted to determine the effect on film thickness ofconducting the spin-on process several times in succession with afurther quantity of synthesis composition added each time. FIG. 7contains SEM micrographs of the top and cross-sectional views of spin-onfilms. FIG. 7(a) is the top view of a film produced by a single spin-on.FIG. 7(b) is a cross-sectional view of the same film. FIGS. 7(c) and7(d) are cross-sectional views of films produced by three and fourspin-ons, respectively. The SEM micrographs show that the spin-on filmof nanocrystals had a smooth surface with a close-packed structure (FIG.7a). The film thickness is uniform and can be controlled by adjustmentof the number of spin-ons. The film thickness was 240, 420 and 540 nmcorresponding to the spin-on number of 1, 3 and 4, respectively.Alternatively the film thickness may be controlled by adjustment of theconcentration of nanocrystals in the ethanol solution.

EXAMPLE 4 Secondary Growth by Microwave Treatment of Films Prepared bySpin-coating of Redispersed MFI Nanocrystals Suspension

Although calcination apparently improves bonding strength amongnanocrystals through condensation/cross-linking of surface hydroxyls,the films produced by spin-on of redispersed crystals may not be adheredstrongly enough to the wafer to withstand mechanical polishing. Inaddition, the existence of large inter-particle mesopores fromnanocrystal packing can be of concern for practical applications. Abrief secondary growth of pure-silica MFI nanocrystals can be conducted,if it is desired to reduce mesopore size, by treating the spin-on filmwith a silicate precursor solution in a microwave oven.

Microwave treatment of the spin-on pure-silica MFI films using asolution of 0.32TPAOH: TEOS: 165H₂O was carried out in a Sharp householdmicrowave oven (700 W). Five grams of solution was used in eachtreatment. The spin-on film was placed horizontally in a 45 mLTeflon-lined Parr autoclave (for microwave use). Power level 1 (10%) wasused. Microwave-treated films were rinsed with deionized water,flow-dried with air and calcined at 450° C. for 2 h under air.

FIG. 8 shows SEM top and cross-sectional micrographs of pure-silica MFIfilms with different microwave treatment times. Film #1 (FIGS. 8a and 8b) was prepared with spin-coating for three times, then treated in amicrowave for 8 minutes. Film #2 (FIGS. 8c and 8 d) was prepared by asingle spin-coating, then microwaved for 10 minutes. Film #3 (FIGS. 8eand 8 f) was prepared by a single spin-coating, then microwaved for 15minutes. The SEM images clearly show that the films became more compactafter microwave treatment and that the compactness increased withincreasing time of microwave treatment. Therefore, it appears that theporosity of these films can be controlled by changing the microwavetreatment time. When the microwave treatment time was shorter than 15minutes, the final film thickness remained unchanged (compare FIGS. 7band 8 d, and FIGS. 7c and 8 b). When the microwave treatment time was to15 minutes, the film became thicker compared to that of the film thathad not been microwaved (compare FIGS. 7b and 8 f). It was observed thatno crystals formed in the bulk phase when the microwave treatment timewas shorter than 15 minutes, while formation of crystals was noticed inthe bulk phase when the microwave treatment time was longer than 15minutes. These results indicated that the secondary growth proceedsinitially by local epitaxy on the deposited nanocrystal (e.g. within 10minutes), and that later in the process, deposition proceeds byincorporation of particles from the solution, together withre-nucleation on the growing film (e.g. longer than 15 minutes).

The SEM images clearly show that inter-crystal voids are reduced bysecondary growth (see FIG. 8b). A polishing experiment indicated thatthe mechanical properties of the final film had been significantlyimproved. Under microwave treatment, the secondary growth producesmaterials primarily within the nanocrystal matrix, and therefore thefinal film thickness remains unchanged at 290 nm (FIG. 8c). The calcinedfilm exhibits a k value of 3.0, which is close to that of the in-situcrystallized film.

IR spectra of spin-on-only film (“a”) and microwave treated (8 minutes)film (“b”) are shown in FIG. 9. It is clear from the figure that theintensity of the characteristic framework vibration of pure-silica MFIincreased due to microwave treatment. The result confirmed a secondarygrowth of spin-on film. Similar results were obtained from X-rayanalyses of the films. FIG. 10 shows X-ray diffraction patterns ofspin-on film before (“a”) and after 8 minutes of microwave treatment(“b”). This figure clearly indicates increasing crystallinity of thespin-on film due to a secondary growth during microwave treatment.

Nitrogen adsorption performed on air-dried nanocrystals after a similarmicrowave treatment (e.g., 8 min) as applied to the spin-on filmrevealed a uniform inter-particle pore size of 22 nm and mesoporousvolume of 0.34 cm³/g. After 4 cycles of 8 min treatment, a uniforminter-particle pore size of 3 nm and an inter-particle pore volume of0.08 cm³/g were obtained. Thus the pore size and volume can also beadjusted by changing the cycle number of microwave treatment.

Polishing experiments indicated that the microwave-treated film stronglyadhered to the substrate. The microwave-treated (8 min), calcined filmexhibited a k value of 3.0 when a normal treatment was applied to washthe film. However, the same film (spin-on film #1) exhibited a muchlower k value of 2.4 when it had been washed by immersing in deionizedwater for 2 days after microwave treatment.

EXAMPLE 5 Effect of Moisture on Zeolite Films

To study the effect of moisture on the k value, films that wereuntreated and that were treated by silylation to improve hydrophobicitywere exposed to ambient air with 60% relative humidity. It has beenreported that vapor phase silylation of pure-silica MFI film can be usedto increase the hydrophobicity of the film. The change in k value wasmonitored against the exposure time.

Silylation (vapor phase) of pure-silica MFI films produced by thespin-on process with redispersed crystals was conducted at 300° C. for 1h using gaseous chlorotrimethylsilane obtained by bubbling nitrogenthrough chlorotrimethylsilane at room temperature. Prior to silylationthe film was dehydrated at 300° C. for 5 h under a flow of nitrogen.After silylation, the system was kept under nitrogen flow at 300° C. foranother 3 h to remove unreacted chlorotrimethylsilane from the film.

FIG. 11 shows the effect of moisture on the spin-on films. The filmthickness was 420 nm. No significant change of k value with exposuretime was seen for an as-synthesized sample. This was expected because ofthe absence of microporosity. The k value was found to be around 2.2.The k value for a calcined sample increased moderately from 2.1 to 3.2(i.e., 50% increase) within an exposure time of 1 hour. There was nosignificant change in the k value with exposure time for a silylatedfilm, and the k value (1.8) was in the ultra low-k range.Microwave-treated film #1 had a k value of 2.2 after silylation.

The effect of moisture on in-situ crystallized pure-silica MFI film alsowas studied. As expected, there was not significant change of the kvalue with exposure time for an as-synthesized sample because of itshydrophobicity and nonporous nature. The k value for a calcined sampleincreased moderately from 2.7 to 3.3 (i.e., 22% increase) within anexposure time of 30 hours (FIG. 3). The k value eventually rose to 3.5after several days. By contrast, moisture is known to have a pronouncedeffect on sol-gel silica and mesoporous silica that has not undergonedehydroxylation treatments (e.g., the k value of mesoporous silicaincreases more than 100% after exposure to moist air.) This clearlyshows that the pure-silica MFI films are more hydrophobic than sol-gelsilica and mesoporous silica. FIG. 3 shows the dependence of the k valueon the exposure time for the silylated sample of in situ crystallizedfilm. The increase of the k value slowed down after silylation, and thek value was lower than that of a calcined non-silylated film having thesame exposure time.

EXAMPLE 6 Production of Spin-on Films with As-synthesized ZeoliteNanoparticle Suspension

This example illustrates the production of a silica zeolite film by thespin-on process, but without conducting separation and redispersion ofthe zeolite nanocrystals. Instead, this step is avoided by conductingthe zeolite production step in the presence of added ethanol or otheralcohol that is produce during the reaction. In this example, a zeolitepure-silican MFI nanoparticle suspension with a range of particle sizeswas synthesized hydrothermally as in Example 2, with the difference thatthe molar composition of the synthesis composition was 0.36 TPAOH/1TEOS/4 EtOH/14.9 H₂O. It is noted that complete in-situ hydrolysis ofTEOS would produce 4 moles of ethanol, so that an equal molar amount ofethanol was added deliberately to the synthesis composition. The clearsolution thus obtained was aged at ambient temperature for 3 daysfollowed by heating in a capped plastic vessel at 80° C. for 3 days.Stirring was provided for both the aging and the heating process. Theresulting colloidal suspension was cooled to room temperature understirring.

The nanoparticle suspension was then centrifuged at 5000 rpm for 20 minto remove large particles, then spun on low resistivity silicon wafers.A Laurell spin coater was used; the spin rate was 3300 rpm for 30 sec.The film was heated in a flow of air at 1° C./min to 450° C. and held atthat temperature for 3 h to bake the film and to remove the organicstructure-directing agent (TPA).

FIG. 12 contains SEM micrographs of the films. The as-deposited filmswere fairly smooth (FIG. 12a). The smoothness could be improved by abrief polishing with 0.05 μm alumina suspension using a Buehler polisher(FIG. 12b). No cracking or film delamination was observed duringpolishing, indicating good mechanical strength of the film and a strongadhesion to the silicon wafer. The film was about 0.33 μm thick (FIG.12c).

Measurements of elastic modulus and hardness were performed using a NanoIndenter® XP and MTS′ Continuous Stiffness Measurement (CSM) technique.With this technique, each indent gives the hardness and elastic modulusas a continuous function of the indenter's displacement into the sample.Loading was controlled such that the loading rate divided by the loadwas held constant at 0.05/sec. Experiments were terminated at a depth of300 nanometers. Ten indentations were performed on each sample. Datafrom the 10 indents on each sample were averaged. The elastic modulus at10% penetration was 16-18 GPa for a 0.42 μm-thick film.

The dielectric constant of the film was measured after thermalevaporation deposition (Denton Vacuum DV-502) of aluminum dots through ashadow mask. Dielectric constant was calculated by measuring capacitanceof a metal-insulator-metal structure as before. Capacitance measurementsshow that calcined spin-on film has a k value of 2.3. The dielectricloss tangent of the film is about 0.02. The k value changes little withfrequency at around 1 MHz (FIG. 14).

The films were exposed to ambient air with 50-60% relative humidity tostudy the effect of moisture adsorption. Change in the k value wasmonitored against the exposure time. The k value increased from 2.3 to3.9 (i.e., 70% increase) within an hour of exposure.

To increase hydrophobicity of the film, vapor phase silylation wasconducted as before. The silylated film had a k value of 2.1, i.e., inthe ultra low-k range. There was only a slight increase in the k valuewith exposure time (FIG. 13b).

For low-k applications, it is important to examine the porosity and poresize distribution of the porous film. FIG. 15 shows nitrogenadsorption-desorption isotherms of two bulk silica samples that havebeen dried with two different procedures. Results of detailed analysisof the isotherms are summarized in Table 1. Clearly both materials havebimodal pore size distribution (e.g., micropore at 0.55 nm and mesoporeat about 2.7-2.8 nm).

TABLE 1 Results of N₂ adsorption for bulk materials from pure-silica MFInanoparticle suspension. All materials calcined under a flow of air at450° C. for 3 hours Micro- Meso- Crys- Dry- Micro- pore Meso- pore tal-ing pore volume pore volume Total Theoret- linity con- size (cm³/g) size(cm³/g) Porosity ical k (%) dition (nm) [a] (nm) [b] (%) [c] [d] [e]Static 0.55 0.17 2.63 0.18 2.4 2.4 64 dry- ing Flow- 0.55 0.17 2.81 0.252.2 2.2 64 air dry- ing [a] Micropore volume was calculated by t-plotmethod. [b] Mesopore volume = total volume − micropore volume. [c]Assuming that the density of the dense material is 2.3 g/cm³. [d]According to Bruggeman's effective medium approximation. [e] By FT-IRanalysis.

It also appears that drying conditions affect the porosity significantlyand thus an appropriate drying procedure should be used. Specifically,drying under convection generates more mesoporosity (0.25 vs. 0.18cm³/g). This result is reasonable if one considers that convectioninduces fast drying, during which the suspension quickly loses fluidityso that the particles settle in position quickly, leading to highermesoporosity. The predicted k value for the silica dried convectivelyfrom Bruggeman's effective medium approximation [Morgan et al., Ann.Rev. Mater. Sci., 30, 645, 2000] is closer to the measured k value (2.2vs. 2.1), suggesting that the silica materials obtained from convectivedrying is more representative of the spin-on film.

X-ray diffraction (XRD) and infrared spectroscopy (IR) have also beenused to characterize the porous silica. Wide angle X-ray diffraction(XRD) pattern suggests the existence of silicalite structure as well asamorphous silica (see FIG. 16). Low angle X-ray diffraction pattern ofthe material (see FIG. 16b) shows a poorly defined peak at 20≈0.83(d=10.64 nm), probably due to the presence of mesopores owing to closepacking of nanoparticles in the material. FT-IR spectrum (absorptionband at about 550 cm⁻¹, not shown) also indicates the presence ofpure-silica MFI zeolite structure and the crystallinity is estimated tobe around 64% by using the intensity ratio of absorption bands at 550and 450 cm⁻¹.

EXAMPLE 7 Production of Surface-patterned Film

Two batches of a zeolite pure-silica MFI nanoparticle suspension with arange of particle sizes were synthesized hydrothermally as in Example 6.One batch (“Batch A”) was then heated at 70° C. for 9 days; the other(“Batch B”) was heated at 80° C. for 3 days. The resulting suspensionswere cooled to room temperature with stirring, and dropped ontohorizontal clean-room grade silicon wafers, forming a liquid film about2 mm thick, having a diameter of 2 cm. Drying at ambient temperaturesproduced surface patterns of the knotted-rope type in the film of BatchA and of the wrinkled-honeycomb type in Batch B. SEM micrographs of thefilms are shown in FIG. 17. The cells were slightly irregular in shape,and the edges were highly wrinkled. Nitrogen desorption measurementsshowed high Brunauer-Emmett-Teller surface areas for both films, andnarrow pore size distributions for both, in both the micropore andmesopore regions.

What is claimed is:
 1. A process for production of a silica zeolite filmon a semiconductor substrate, comprising: (a) combining a silica sourceselected from organic silica sources and inorganic silica sources withan organic hydroxide zeolite-structure-directing agent (SDA) and waterto produce a zeolite synthesis composition containing thestructure-directing agent, the silica source and water, in a molar ratioof x SDA: 1 silica source: y H₂O, wherein the value of x is from about0.2 to about 0.6 and the value of y is from about 100 to about 200; (b)contacting the substrate to be coated with the synthesis composition;and (c) heating the substrate and synthesis composition from step (b) toproduce a silica zeolite film on the substrate.
 2. A process accordingto claim 1 in which the value of x is from about 0.2 to about 0.45 andthe value of y is from about 140 to about
 180. 3. A process according toclaim 1 in which the value of x is 0.32 and the value of y is
 165. 4. Aprocess according to claim 1 in which the silica source is a C₁-C₂ alkylorthosilicate.
 5. A process according to claim 1 in which the silicasource is selected from fumed silica, silica gel and colloidal silica.6. A process according to claim 1 in which the structure-directing agentis a quaternary ammonium hydroxide.
 7. A process according to claim 1 inwhich the silica source is ethyl orthosilicate and thestructure-directing agent is tetrapropylammonium hydroxide.
 8. A processaccording to claim 1 further comprising (d) heating the substrate andfilm of step (c) to a temperature of from about 350 to about 550° C. 9.A process according to claim 1 further comprising treating the silicafilm of step (d) to remove surface hydroxyl groups therefrom.
 10. Aprocess according to claim 1 in which the silica zeolite is ahigh-silica MFI zeolite.
 11. A process according to claim 1 in which thesilica zeolite is a pure-silica MFI zeolite.
 12. A process according toclaim 1 in which the semiconductor substrate is a silicon wafer or agallium arsenide wafer.
 13. A process according to claim 1 in which thesubstrate comprises a silicon wafer or a gallium arsenide wafer and oneor more metal layers or structures located on said wafer.
 14. Asemiconductor substrate having at least one silica zeolite film thereonproduced by a process according to claim
 1. 15. A semiconductorsubstrate according to claim 1 in which the at least one silica zeolitefilm is a pure-silica zeolite film.
 16. A process for the production ofa silica zeolite film on a semiconductor substrate, comprising: (a)combining a silica source selected from organic silica sources andinorganic silica sources with an organic hydroxidezeolite-structure-directing agent (SDA) and water to produce a zeolitesynthesis composition containing the structure-directing agent, thesilica source and water in a molar ratio of x₁ SDA: 1 silica source: y₁H₂O, wherein the value of x₁ is from about 0.2 to about 0.5 and thevalue of y₁ is from about 5 to about 30; (b) heating the composition ofstep (a) to produce an aqueous colloidal suspension of silica zeolitecrystals; (c) separating the crystals from the product of step (b) (d)dispersing the separated crystals from step (c) in a dispersing agent toform a suspension of the crystals in the dispersing agent, (e)depositing the crystal suspension of step (d) on a semiconductorsubstrate; and (f) rotating the substrate from step (e) under conditionsso as to produce a silica zeolite film thereon by spin-coating.
 17. Aprocess according to claim 16 in which the value of x₁ is from about 0.3to about 0.4 and the value of y₁ is from about 10 to about
 20. 18. Aprocess according to claim 16 in which the value of x₁ is 0.36 and thevalue of y₁ is 14.29.
 19. A process according to claim 16 in which thesilica source is a C₁-C₂ alkyl orthosilicate.
 20. A process according toclaim 16 in which the silica source is selected from fumed silica,silica gel and colloidal silica.
 21. A process according to claim 16 inwhich the structure-directing agent is a quaternary ammonium hydroxide.22. A process according to claim 16 in which the silica source is ethylorthosilicate and the structure-directing agent is tetrapropylammoniumhydroxide.
 23. A process according to claim 1 further comprising (g)heating the film of step (f) to a temperature of from about 350 to about550° C.
 24. A process according to claim 23 further comprising treatingthe silica film of step (g) to remove surface hydroxyl groups therefrom.25. A process according to claim 16 in which the silica zeolite is ahigh-silica MFI zeolite.
 26. A process according to claim 16 in whichthe silica zeolite is a pure-silica MFI zeolite.
 27. A process accordingto claim 16 in which the semiconductor substrate is a silicon wafer or agallium arsenide wafer.
 28. A process according to claim 16 in which thesubstrate comprises a silicon wafer or a gallium arsenide wafer and oneor more metal layers or structures located on said wafer.
 29. Asemiconductor substrate having at least one silica zeolite film thereonproduced by a process according to claim
 16. 30. A semiconductoraccording to claim 29 wherein the at least one silica zeolite film is apure-silica MFI zeolite film.
 31. A process for the production of asilica zeolite film on a semiconductor substrate, comprising: (a)combining a silica source selected from organic silica sources andinorganic silica sources with an organic hydroxidezeolite-structure-directing agent (SDA), water, and an alkanol selectedfrom ethanol and methanol, to produce a zeolite synthesis compositioncontaining the structure-directing agent, silica source, water andalkanol in a molar ratio of x₂ SDA: 1 silica source: y₂ H₂O: z₂ alkanol,wherein the value of x₂ is from about 0.2 to about 0.5, the value of y₂is from about 10 to about 20, and the value of z₂ is from about 1 toabout 30; (b) heating the composition of step (a) to produce an aqueouscolloidal suspension of silica zeolite crystals; (c) depositing thecrystal suspension of step (b) on a semiconductor substrate; and (d)rotating the substrate from step (c) under conditions so as to produce asilica zeolite film thereon by spin coating.
 32. A process according toclaim 31 in which the value of x₂ is from about 0.3 to about 0.4, andthe value of y₂ is from about 12 to about
 18. 33. A process according toclaim 31 in which the value of x₂ is 0.36, the value of y₂ is 14.29, andthe value of z₂ is 4.0.
 34. A process according to claim 31 in which thesilica source is a C₁-C₂ alkyl orthosilicate.
 35. A process according toclaim 31 in which the silica source is selected from fumed silica,silica gel and colloidal silica.
 36. A process according to claim 31 inwhich the structure-directing agent is a quaternary ammonium hydroxide.37. A process according to claim 31 in which the silica source is ethylorthosilicate, the template is tetrapropylammonium hydroxide, and thealkanol is ethanol.
 38. A process according to claim 31 furthercomprising (e) heating the film of step (d) to a temperature of fromabout 350 to about 550° C.
 39. A process according to claim 38 furthercomprising treating the silica film of step (e) to remove surfacehydroxyl groups therefrom.
 40. A process according to claim 31 in whichthe silica zeolite is a high-silica zeolite.
 41. A process according toclaim 31 in which the silica zeolite is a pure-silica MFI zeolite.
 42. Aprocess according to claim 31 in which the semiconductor substrate is asilicon wafer or a gallium arsenide wafer.
 43. A process according toclaim 31 in which the substrate comprises a silicon wafer or a galliumarsenide wafer and one or more metal layers or structures located onsaid wafer.
 44. A semiconductor substrate having at least one silicazeolite film thereon produced by a process according to claim
 31. 45. Asemiconductor substrate according to claim 44 in which the at least onesilica zeolite film is a pure-silica MFI zeolite film.
 46. A process forproducing a patterned silica zeolite film on a semiconductor substrate,comprising: (a) combining a silica source selected from organic silicasources and inorganic silica sources with an organic hydroxidezeolite-structure-directing agent (SDA), water, and an alkanol selectedfrom ethanol and methanol, to produce a zeolite synthesis compositioncontaining the structure-directing agent, silica source, water andalkanol in a molar ratio of x₃ SDA: 1 silica source: y₃ H₂O: z₃ alkanol,wherein the value of x₃ is from about 0.2 to about 0.5, the value of y₃is from about 10 to about 20, and the value of z₃ is from about 1 toabout 30; (b) heating the composition of step (a) to produce an aqueouscolloidal suspension of silica zeolite crystals; (c) depositing thecrystal suspension of step (b) on a semiconductor substrate; and (d)drying the crystal suspension at ambient temperature to produce apatterned silica zeolite film.
 47. A process according to claim 46 inwhich the value of z₂ 4.0.
 48. A process according to claim 46 in whichthe silica source is a C₁-C₂ alkyl orthosilicate.
 49. A processaccording to claim 46 in which the structure-directing agent is aquaternary ammonium hydroxide.
 50. A process according to claim 46 inwhich the silica source is ethyl orthosilicate, the template istetrapropylammonium hydroxide, and the alkanol is ethanol.
 51. A processaccording to claim 46 in which the silica zeolite is a high-silicazeolite.
 52. A process according to claim 46 in which the silica zeoliteis a pure-silica MFI zeolite.
 53. A process according to claim 46 inwhich the semiconductor substrate is a silicon wafer or a galliumarsenide wafer.
 54. A process according to claim 46 in which thesubstrate comprises a silicon wafer or a gallium arsenide wafer and oneor more metal layers or structures located on said wafer.